In a motor vehicle, transfer gears are used to distribute the drive torque in a variable manner to the two vehicle axles. For this purpose, the transfer gear has an input shaft, a first output shaft and a second output shaft. The input shaft is connected to a drive unit of the motor vehicle, e.g. an internal combustion engine. The first output shaft is connected to a first axle of the motor vehicle, e.g. the rear axle, in particular via a first axle differential. The second output shaft is connected to a second axle of the motor vehicle, e.g. the front axle, in particular via a second axle differential.
The transfer gear furthermore has a torque transmission device, which has a clutch in order to distribute a drive torque introduced via the input shaft selectively to the first output shaft and the second output shaft. For example, the first output shaft can be of one-piece design with the input shaft or can be connected thereto for conjoint rotation, wherein a friction clutch couples the input shaft selectively also to the second output shaft in a variable manner. As an alternative, it is possible, for example, for the torque transmission device to comprise an interaxle differential, wherein a friction clutch acts between the input shaft and one of the two output shafts (or between both output shafts) in order to lock the interaxle differential selectively in a variable manner.
The input shaft and the second output shaft are generally arranged at different heights, wherein an offset drive is provided between the torque transmission device and the second output shaft. Said offset drive can be designed as a chain drive, which has a lower chain wheel and an upper chain wheel, which are connected by means of a chain. The lower chain wheel is coupled for conjoint rotation to the second output shaft. The upper chain wheel is coupled for conjoint rotation to an output element of the torque transmission device.
To eliminate the need for the transfer gear to have a dedicated oil pump, the chain of the chain drive can serve as an oil delivery device. For this purpose, the lower chain wheel dips into an oil sump filled with lubricating oil, wherein lubricating oil is conveyed out of the oil sump in the direction of the upper chain wheel by means of the chain. At the upper end of the chain drive, the lubricating oil is thrown off the chain and can then be collected by a collecting device, for example, and passed from there in the direction of the lubrication points (e.g. friction clutch and bearings).
One disadvantage of known transfer gears is that the lower chain wheel, which dips into the oil sump, and the chain passed through the oil sump cause unwanted churning losses, i.e. drag torques arising in the oil sump reduce the efficiency of the transfer gear. Moreover, this increases the temperature of the lubricating oil in the oil sump, impairing the cooling effect of the lubricating oil.
WO 2012/038022 discloses a transfer gear which, in the oil reservoir, has an outlet opening which opens into the oil sump, wherein the chain is arranged on the outlet opening of the oil reservoir in such a way that the chain restricts the outflow of the lubricating oil collected in the oil reservoir into the oil sump.
In view of continuously increasing demands on the energy efficiency of motor vehicles, it is an object of the present invention to provide a transfer gear of the type described above which, while being of robust and reliable construction, exhibits less loss due to churning of the chain drive in oil.
The lower losses due to churning are advantageously achieved through a reduced oil level, which can be set by an actuable adjusting mechanism.
It is advantageous here if the actuable adjusting device is triggered by means of a torque transmission device, ensuring that the oil supply is initiated only when required.